High-Strength, Fast Self-Healing, Aging-Insensitive Elastomers with Shape Memory Effect

Robust, transparent, self-healable, recyclable all-starch-based gel with thermoelectric capability for wearable sensor

Conventional all-starch-based (ASB) gels are weak and lack ductility. The preparation of a robust ASB gel with multi-functionalities e.g., self-healing, anti-freezing, conductivity, and so forth, is highly desirable but challenging. Herein, a new kind of ASB gel was prepared by gelatinizing starch in urea and choline chloride solution (UC) with the aid of water. Its tensile strength was up to 1.08 MPa with a tensile strain of 313 %, and this value hardly changed after 10 days ageing. A high healing efficiency of 98 % can be achieved after 1 h of healing at room temperature, and the healed tensile strength reaches up to ca. 1.06 MPa, which is almost the highest value for ASB gel. The resultant ASB gel can surfer from bending and twisting at -80 °C. Moreover, ASB gel also exhibits excellent biocompatibility and biodegradability. In addition, UC endowed the ASB gel with ion conductivity, allowing it to be used as a flexible strain sensor to monitor human movement. The ion-conductive ASB gel also exhibited thermoelectric ability with a Seebeck coefficient of 2.5 mV K-1, which can be further improved to 5 mV K-1 with a maximum output voltage of 252 mV by introducing a gradient of ionic concentration.

Functionalized TMC and ε-CL elastomers with shape memory and self-healing properties

Introduction: Smart elastomers, which possess self-healing and shape memory capabilities, have immense potential in the field of biomedical applications. Polycarbonates and polyesters have gained widespread interest due to their remarkable biocompatibility over the last century. Nevertheless, the lack of functional versatility in conventional polyesters and polycarbonates means that they fall short of meeting the ever-evolving demands of the future. Methods: This paper introduced a new smart elastomer, named mPEG43-b-(PMBC-co-PCL)n, developed from polyester and polycarbonate blends, that possessed shape memory and self-heal capabilities via a physical crosslinking system. Results: The material demonstrated a significant tensile strength of 0.38 MPa and a tensile ratio of 1155.6%, highlighting its favorable mechanical properties. In addition, a conspicuous shape retrieval rate of 93% was showcased within 32.5 seconds at 37°C. Remarkably, the affected area could be repaired proficiently with no irritation experienced during 6h at room temperature, which was indicative of an admirable repair percentage of 87.6%. Furthermore, these features could be precisely modified by altering the proportion of MBC and ε-CL to suit individual constraints. Discussion: This innovative elastomer with exceptional shape memory and self-heal capabilities provides a solid basis and promising potential for the development of self-contracting intelligent surgical sutures in the biomedical field.

Chemically Recyclable Biobased Non-Isocyanate Polyurethane Networks from CO2 -Derived Six-membered Cyclic Carbonates

Non-isocyanate polyurethanes (NIPUs) are widely studied as sustainability potential, because they can be prepared without using toxic isocyanates in the synthesis process. The aminolysis of cyclic carbonate to form NIPUs is a promising route. In this work, a series of NIPUs is prepared from renewable bis(6-membered cyclic carbonates) (iEbcc) and amines. The resulting NIPUs possess excellent mechanical properties and thermal stability. The NIPUs can be remolded via transcarbamoylation reactions, and iEbcc-TAEA-10 (the molar ratio of tris(2-aminoethyl)amine in amines is 10%) still get a recovery ratio of 90% in tensile stress after three cycles of remolding. In addition, the obtained materials can be chemically degraded into bi(1,3-diol) precursors with high purity (>99%) and yield (>90%) through alcoholysis. Meanwhile, the degraded products can be used to regenerate NIPUs with similar structures and properties as the original samples. The synthetic strategy, isocyanate-free and employing isoeugenol and carbon dioxide (CO2 ) as building blocks, makes this approach an attractive pathway to NIPU networks taking a step toward a circular economy.

Vapor-phase synthesis of a reagent-free self-healing polymer film with rapid recovery of toughness at room temperature and under ambient conditions

A rapidly self-healable polymer is highly desirable but challenging to achieve. Herein, we developed an elastomeric film with instant self-healing ability within 10 s at room temperature. For this purpose, a series of copolymers of poly(glycidyl methacrylate-co-2-hydroxyethyl acrylate) (poly(GMA-co-HEA), or pGH) were synthesized in the vapor phase via an initiated chemical vapor deposition (iCVD) process. The elastomer includes a large amount of hydroxyl groups in the 2-hydroxyethyl acrylate (HEA) moiety capable of forming rapid, reversible hydrogen bonding at room temperature, while glycidyl methacrylate (GMA) with a rigid methacrylic backbone chain in the copolymer provides mechanical robustness to the elastic copolymer. With the optimized copolymer composition, pGH indeed showed instant recovery of the toughness within a minute; a completely divided specimen could be welded within a minute at room temperature and under ambient conditions simply by placing the pieces in close contact, which showed the outstanding recovery performance of elastic modulus (93.2%) and toughness (15.6 MJ m^-3). The rapid toughness recovery without supplementing any external energy or reagents (e.g. light, temperature, or catalyst) at room temperature and under ambient conditions will be useful in future wearable electronics and soft robotics applications.

Double-Network Luminescent Films Constructed Using Sulfur Quantum Dots and Lanthanide Complexes

Although UV light-switchable luminescent films are of importance for application in soft optical devices and anticounterfeiting labels, there are still challenges in developing such films integrated with outstanding luminescent property, high self-healing efficiency, and simultaneously excellent mechanical strength. Herein, double-network (DN) luminescent films are designed and constructed via an intermolecular hydrogen bond crosslinking strategy of poly(ethylene glycol) (PEG) in sulfur quantum dots (S-QDs) and polyurethane (PU), where S-QDs ("stone" one) play dual roles of acting both as a soft segment to crosslink another segment PU ("bird" one) and also as the origin of a luminescence center ("bird" two) in films. In addition, lanthanide(III) complexes (LnCs, Ln═Eu³⁺, Tb³⁺) are employed as another emission source to embed in the films and switch the emission colors of DN films from the multicolor (red-yellow-green) of LnCs to the blue color of S-QDs by changing the ultraviolet excitation wavelength from 254 to 365 nm. It is worth noting that the crosslinking network strategy can effectively prevent S-QDs and LnCs from aggregating or leaking and enable both luminescence centers to homogeneously distribute, resulting in luminescent DN films possessing extraordinary UV light-switchable luminescence, improved mechanical property, and excellent self-healing ability. This work presents a viable method for the design and fabrication of luminescent films with multifunctional applications in flexible robotics, wearable devices, and dual-luminescent anticounterfeiting materials.

Mechano-Regulable and Healable Silk-Based Materials for Adaptive Applications

Mechanically adaptive materials responsive to environmental stimuli through changing mechanical properties are highly attractive in intelligent devices. However, it is hard to regulate the mechanical properties of most mechanically adaptive materials in a facile way. Moreover, it remains a challenge to achieve mechano-regulable materials with mechanical properties ranging from high strength to extreme toughness. Here, inspired by the reversible nanofibril network structure of skeletal muscle to achieve muscle strength regulation, we present a mechano-regulable biopolymeric silk fibroin (SF) composite through regulating dynamic metal-ligand coordination bonds by using water molecules as competitive regulators. Efficient interfacial hydrogen bonds between tannic acid-tungsten disulfide nanohybrids and the SF matrix endow the composite with high mechanical strength and self-healing ability. The resulting composite exhibits 837-fold change in Young's modulus (5.77 ± 0.61 GPa to 6.89 ± 0.64 MPa) after water vapor triggering, high mechanical properties (72.5 ± 6.3 MPa), and excellent self-healing efficiency (nearly 100%). The proof-of-concept ultraconformable iontronic skin and smart actuators are demonstrated, thereby providing a direction for future self-adaptive smart device applications.

Advances and Challenges of Self-Healing Elastomers: A Mini Review

In the last few decades, self-healing polymeric materials have been widely investigated because they can heal the damages spontaneously and thereby prolong their service lifetime. Many ingenious synthetic procedures have been developed for fabricating self-healing polymers with high performance. This mini review provides an impressive summary of the self-healing polymers with fast self-healing speed, which exhibits an irreplaceable role in many intriguing applications, such as flexible electronics. After a brief introduction to the development of self-healing polymers, we divide the development of self-healing polymers into five stages through the perspective of their research priorities at different periods. Subsequently, we elaborated the underlying healing mechanism of polymers, including the self-healing origins, the influencing factors, and direct evidence of healing at nanoscopic level. Following this, recent advance in realizing the fast self-healing speed of polymers through physical and chemical approaches is extensively overviewed. In particular, the methodology for balancing the mechanical strength and healing ability in fast self-healing elastomers is summarized. We hope that it could afford useful information for research people in promoting the further technical development of new strategies and technologies to prepare the high performance self-healing elastomers for advanced applications.

High-strength, high-toughness, self-healing thermosetting shape memory polyurethane enabled by dual dynamic covalent bonds

Smart materials that integrate multiple functions into one system will broaden the application range of materials, but there are still challenges to obtain a material with excellent shape memory, toughness,...

Advances in Injectable and Self-healing Polysaccharide Hydrogel Based on the Schiff Base Reaction

Injectable hydrogel possesses great application potential in disease treatment and tissue engineering, but damage to gel often occurs due to the squeezing pressure from injection devices and the mechanical forces from limb movement, and leads to the rapid degradation of gel matrix and the leakage of the load material. The self-healing injectable hydrogels can overcome these drawbacks via automatically repairing gel structural defects and restoring gel function. The polysaccharide hydrogels constructed through the Schiff base reaction own advantages including simple fabrication, injectability, and self-healing under physiological conditions, and therefore have drawn extensive attention and investigation recently. In this short review, the preparation and self-healing properties of the polysaccharide hydrogels that is established on the Schiff base reaction are focused on and their biological applications in drug delivery and cell therapy are discussed.

Basic Approaches to the Design of Intrinsic Self-Healing Polymers for Triboelectric Nanogenerators

Triboelectric nanogenerators (TENGs) as a revolutionary system for harvesting mechanical energy have demonstrated high vitality and great advantage, which open up great prospects for their application in various areas of the society of the future. The past few years have seen exponential growth in many new classes of self-healing polymers (SHPs) for TENGs. This review presents and evaluates the SHP range for TENGs, and also attempts to assess the impact of modern polymer chemistry on the development of advanced materials for TENGs. Among the most widely used SHPs for TENGs, the analysis of non-covalent (hydrogen bond, metal-ligand bond), covalent (imine bond, disulfide bond, borate bond) and multiple bond-based SHPs in TENGs has been performed. Particular attention is paid to the use of SHPs with shape memory as components of TENGs. Finally, the problems and prospects for the development of SHPs for TENGs are outlined.